Right-Lane Closure With a Crest, a Driveway, and a Crosswalk
A four-lane undivided arterial, 45 mph posted, with 12-ft lanes and 12,000 vehicles per day, needs a right-lane closure for three days to replace a storm drain inlet. The work area is 180 ft long. About 350 ft upstream of where the taper would begin, the road crosses a crest that limits sight distance to roughly 400 ft. A commercial driveway enters the right lane 60 ft downstream of the work area, and a marked crosswalk with a pedestrian signal is 200 ft upstream. The contractor proposes to set the advance warning signs at the standard 45 mph spacing, use cones for the taper, and keep the closure in place from 9 a.m. to 3 p.m. only. No flaggers are proposed, and the plan shows no buffer space between the taper and the work area.
1. Compute the merging taper length and describe the layout you would require.
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Merging taper: L = W x S for 45 mph and below, so 12 ft x 45 = 540 ft. That is the taper the contractor must install, not the 180 ft of work area.
Layout from the upstream end:
- Advance warning signs at the MUTCD 45 mph spacing, using the table value rather than memory, plus a second sign beyond the crest because a sign at the normal distance is hidden from a driver approaching the crest.
- A merging taper of 540 ft ending at the lane closure.
- Buffer space between the taper and the work area, with workers and equipment kept out of it.
- The work area, then the downstream taper.
- Channelizing devices at the 45 mph spacing, with taper devices closer together than tangent devices.
Because the crest is only 350 ft from the taper, a driver can see the cone line with far less than the 540-ft taper length. Sight distance, not cone spacing, is the layout's critical defect.
2. Identify the deficiencies in the contractor's proposal and rank them by risk.
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Rank by risk:
- Sight distance at the crest. A driver at 45 mph cresting with 350 ft of view has roughly four to five seconds, not enough to perceive, decide, and merge. Add signing beyond the crest and consider a flagger or temporary signal if traffic will not gap.
- The 540-ft taper versus the proposed layout. A short taper turns the merge into a surprise at the work area.
- The driveway 60 ft downstream. A vehicle entering the right lane meets the work area immediately. The driveway must stay open with a clear path or be closed with proper notice, and equipment must not be stacked across it.
- The crosswalk 200 ft upstream. Pedestrians must not be channelized into the taper or the closed lane.
- The 9 a.m. to 3 p.m. window. It avoids peaks, which is good, but daily setup and removal is when the crew is most exposed.
3. How would you handle the driveway, the crosswalk, and the 9 a.m. to 3 p.m. window?
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Driveway: keep it open if possible, with the closure laid out so a vehicle can enter and exit, and post an entrance sign if the cone line obscures it. If it cannot stay open, coordinate with the property owner and give advance notice. Do not let a resident or truck driver discover the closure at the last second.
Crosswalk: maintain a protected pedestrian path, keep the crosswalk, push button, and pedestrian signal visible, and place no cones or equipment in the crosswalk. If the work blocks the accessible route, provide a temporary accessible route.
Work window: the 9 a.m. to 3 p.m. window reduces exposure to peak traffic, but daily setup and takedown doubles the number of times workers are in the lane. Require a written setup sequence, a spotter, and high-visibility apparel. Put signs out before cones and pick cones up before signs, and never leave a partial closure overnight.
If the work cannot be completed in three days, replan the work rather than extending the daily window into the peak period.